Going Solar – Part 8: Through the first year

It has now been 1 year since my system started producing electricity, which seems to be a good point to stop and look back over the data.

System overview:

The system is a 2.7 kW (DC) / 2.3 kW (AC) rated installation featuring 10 Solarworld Sunmodule Plus SW270 Mono Black panels, each rated at 270 Watts (DC) and a SolarEdge SE5000A-US inverter with P300 panel optimizers.  It is roof mounted  with a pitch of 18.5 degrees and array azimuth of 235 degrees.  There is a mountain behind the house which delays the start of sun hitting the roof for an hour or so after nominal sunrise. The installed cost of the system was $11,125.


In it’s first year the system produced 5.1 MWh of AC electricity. Highest production was in May with 566 kWh, lowest production was December with 273 kWh but January was only 4 kWh better.  The production suffered a bit in the June – September time frame with the high temperatures associated with a desert summer as well as a couple of weeks where smoke from nearby forest fires at least partially obscured the sun, and December through early February have been abnormally cloudy.  Given where the system is located, though, I’m pretty happy with the production overall.



I do not have a revenue meter installed in my inverter, but my utility website allows me to go back and see detailed usage data which provides a reasonable substitute. As mentioned in my earlier posts on this topic I wanted to have a system that fully covered my highest day usage and allowed me to shift from using a water-based swamp cooler for summer cooling to the electric air conditioning, or a larger system since I had space and budget to do so, but the utility would only allow a system sized off of the billed usage for the prior 12 moths, and since I had been as electrically efficient as I could be during that period I found myself not being able to install the  system I desired.  That being said, and against the background of having only run the air conditioner 2 days (when the smoke from nearby fires was too heavy to have the windows open at night), I have come out just slightly ahead on production relative to usage based on the currently available data – on the order of < 50 kWh. Because my dominant energy usage is winter heating rather than summer cooling, whatever gains I make in the summer are quickly eroded once the shorter days and higher electricity usage of the winter comes into play – and I’m not even on electric heat.  Nearly any usage of air conditioning in the summer would push it the other way.



Pricing the value of the generated electricity is a difficult task because of the rate structure the utility uses – there is a base rate per kWh for a nominal average use, which varies between summer and winter seasons, and a higher rate for usage over and above that.  Further complicating matters is that the rate structure was recently changed, and then the element of minimum connection charges comes in.  With my utility the minimum fee is nominally $10 a month if you use below a certain amount of grid generated electricity, which creates the slightly interesting ethical dilemma of having a sweet spot where if you are running close to even for a month it may be economically advantageous to waste electricity for a day or two and come in just over the minimum usage requirement which, when billed, is about $4.  Then comes in the range of possible net metering agreements, where some utilities create a cash balance for excess production at a different rate than for consumption, others (such as mine) carry a rolling kWh balance, and charge any fees separately, etc…

The approach I am taking is to make the overly simplistic assumption that I come out even on usage vs. generation on a monthly basis (which per the chart above can be seen as a false assumption) and to use a weighted average of the baseline usage allowance (which again is a false assumption, as the baseline is higher in the summer and lower in the winter, which is opposite my usage pattern).  Using that simplistic approach, and calculating for the different rate structures in place at the time, I calculate that the overall value of the my first year production was right around $850.

So in the end where does that put me in terms of a return on investment?  I paid roughly $100 in minimum usage fees to the utility (thanks to a couple of months where I fell into that sweet spot of using just enough extra to not be subject to the minimum fee but for the billed amount to be below it anyway), resulting in a calculated net value of $750.  Given the 30% federal tax credit which applied to my system installation (and which I have claimed and received) my overall system cost ends up being right around $7800.  That comes out to a 9.6% return, and given the amount of assumptions involved not justifying anything beyond a whole number precision I’ll round it to 10% – which clearly beats the 0.05% APR I was getting in the savings account I pulled the money out of to pay for the system.

Overall wrap-up of year 1:

All in all I am very happy with the system.  While it is in no way hidden, it doesn’t look in any way awkward on the roof, and in fact the amount of shade it provides helps to reduce the attic heat buildup during the summer.  There has been no maintenance required or performed, but in hindsight I potentially could have rinsed some of the accumulated dust off in the middle of summer as there was a slight increase in production visible for a period after the one rain shower which passed through during the otherwise dry and dusty summer. Having the SolarEdge internet connected inverter and optimizers has been an excellent decision as I’ve been able to not only monitor overall production but I can also go in and see real time panel by panel operation, which allowed me to identify that the shade tree I thought might obscure some of the panels does not do so, so there was no need to trim it back.

Having already touched on it multiple times, I’ll once again express my displeasure about the utility’s sizing policy.  I have space and budget to go bigger, and their published network capability would allow me to nearly quadruple my installation without requiring any equipment upgrades on their side of the connection – and in fact there are several houses in my area that do have systems of that size or larger. With a larger system, which I am very willing to install at my expense, I could personally make more responsible use of this area’s resources by shifting from water based to electric based summer cooling, as well as generate excess during the exact periods where they publicly claim there are shortages.  But the real goal of  most US utilities is to turn a profit rathar than encourage responsible generation and usage, and my several requests to expand have fallen on deaf ears.

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